1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having an SR flip flop circuit.
2. Background Art
With the recent popularization of portable terminals, the demand for a smaller and less power-consuming semiconductor device is growing. Therefore, the importance of non-volatile memories in the portable terminals is also rising.
Non-volatile memories currently in practical use include flash memories and ferroelectric memories. For example, portable terminals, which are required to have a small size, have a non-volatile memory mounted on a silicon device.
Flip flops, which are commonly used in silicon devices, lose the value stored therein when the current supplied thereto is interrupted. Thus, the flip flops require an additional circuit or manipulation to restore the internal state when power is turned on. This leads to a longer time for the flip flops to start operation.
There has been proposed a non-volatile flip flop in which one of a pair of non-volatile variable resistor elements is made to have a higher resistance, and the other is made to have a lower resistance in a storage operation, one of a pair of storage nodes is set at a higher potential, and the other is set at a lower potential according to the difference between the resistances of the pair of non-volatile variable resistor elements in a recall operation, and the pair of non-volatile variable resistor elements are made of a phase change material that has a higher resistance in an amorphous state and has a lower resistance in a crystal state (see Japanese Patent No. 3768504, for example).
In the conventional flip flop, the resistance of the non-volatile variable resistor elements varies with the phase change caused by heating. Therefore, the voltage pulse width applied for heating has to be finely controlled, for example.